In dental treatments with current pneumatic handpieces, a tool tip or burr is rotated at a speed higher than the desired cutting speed. These speeds can be as high as 450,000 revolutions per minute (rpm). When cutting load is applied, this pneumatic system is slowed significantly, adversely affecting cutting capability. The dental practitioner must maintain a useful system speed for cutting by carefully balancing cutting load and pneumatic pressure in order to properly accomplish the cutting operation. Water is also typically provided during the cutting operation to cool the cutting surface as well as the tool surface.
Knowledge of the speed of the rotating burr and/or the rotating turbine under load is desirable and necessary to control speed at a useful value. Prior art devices detect the rotating speed of a pneumatic handpiece by a magnetic resistance element, or elastic control elements assembled near the tool tip.
For example, U.S. Pat. No. 5,567,154 issued to Wohlgemuth on Oct. 22, 1996, entitled “Dental Turbine Drive Having Means of Automatic Speed Control,” (the '154 patent) and U.S. Pat. No. 5,496,173 issued to Wohlgemuth on Mar. 5, 1996, entitled “Dental Handpiece Having an Automatically Controlled Turbine Drive,” (the '173 patent) both disclose speed control by a control element in the form of a proportional valve placed in an air turbine exhaust path that throttles open as the turbine speed is decreased due to lowered centrifugal force on an elastic element, and conversely throttles closed as the turbine speed is increased. The control element adds cost and complexity to the handpiece. Such a control element also is subject to degradation during sterilization of the handpiece. The '154 patent further includes as a second element a pressure chamber that responds to changes in pressure to further support the control element. Devices incorporating these features are currently being marketed.
U.S. Pat. No. 4,493,643 issued Jan. 15, 1985, to Tachibana, entitled “Dental Handpiece Having Non-contact Rotational Speed Detection Device” (the '643 patent) discloses speed detection by a cylindrical rotor of magnetic material and coil windings to produce an induction pulse generator. Such detection means adds cost and complexity to the handpiece and also is subject to degradation during required sterilization of the handpiece.
U.S. Pat. No. 3,865,505 issued to Flatland on Feb. 11, 1975, entitled “Speed Governor for a Dental Handpiece,” (the '505 patent) discloses speed control by a proportional bypass valve placed in the turbine supply path that throttles open as the turbine speed is decreased due to lowered discharge pressure in the exhaust channel, and conversely throttles closed as the turbine speed is increased. It too is inferior because it adds cost and complexity to the handpiece, and its control apparatus is subject to degradation during sterilization of the handpiece. Devices incorporating these features are currently being marketed.
These prior art methods are impractical or undesirable as they add cost to the handpiece. These devices also can require relatively large structures within the handpiece, making them difficult and uncomfortable to hold, while also leading to integration problems as a result of this bulky but required size. Depending on the design, the sensors/control elements of these prior art units also can be difficult to protect from damage during handpiece sterilization. What is desired is a detection system that remotely detects the drill speed and regulates the drill speed based on the detected drill speed. Such a system does not rely on detecting exhaust pressure to determine rotational speed. Ideally, the detection system is not subject to damage as a result of handpiece sterilization.